Many vessels in animals transport fluids from one body location to another. Frequently, fluid flows in a substantially unidirectional manner along the length of the vessel. For example, veins in the body transport blood to the heart and arteries carry blood away from the heart.
It is often desirable to retract the wall of a body vessel to correct or mitigate undesirable medical conditions, such as correcting compromised function of sphincter muscles or valves within a body vessel. Certain medical conditions are ameliorated by restricting the caliber of portions of a body vessel, such as the esophagus, urethra, ureter, bile duct, or a vein. For example, restriction of a body vessel near a defective sphincter muscle may improve or restore sphincter function. Several undesirable medical conditions can result from the inability of sphincter muscles to close completely. Gastroesophageal reflux disease (GERD) involves a deficiency of the pyloric sphincter, leading to the regurgitation of stomach contents into the esophagus or diaphragm. Urinary incontinence and/or vesicoureteral reflux can result from malfunction of sphincter muscles surrounding the urethra or ureters. Retraction of portions of the esophagus, ureters, urethra, or other body vessels may advantageously improve sphincter function associated with these vessels.
Furthermore, restriction of a body vessel may improve the function of defective valves within the body vessel. In many body vessels, including mammalian veins, natural valves are positioned along the length of the vessel in the form of leaflets disposed annularly along the inside wall of the vein which open to permit blood flow towards the heart and close to restrict back flow. These natural venous valves open to permit the flow of fluid in the desired direction, and close upon a change in pressure, such as a transition from systole to diastole. When blood flows through the vein, the pressure forces the valve leaflets apart as they flex in the direction of blood flow and move towards the inside wall of the vessel, creating an opening therebetween for blood flow. The leaflets, however, do not normally bend in the opposite direction and therefore return to a closed position to restrict or prevent blood flow in the opposite, i.e. retrograde, direction after the pressure is relieved. The leaflet structures, when functioning properly, extend radially inwardly toward one another such that the tips contact each other to restrict backflow of blood.
In the condition of venous valve insufficiency, the valve leaflets do not function properly. Incompetent venous valves can result in symptoms such as swelling and varicose veins, causing great discomfort and pain to the patient. If left untreated, venous valve insufficiency can result in excessive retrograde venous blood flow through incompetent venous valves, which can cause venous stasis ulcers of the skin and subcutaneous tissue. Venous valve insufficiency can occur in the superficial venous system, such as the saphenous veins in the leg, or in the deep venous system, such as the femoral and popliteal veins extending along the back of the knee to the groin.
Recently, various intraluminally implantable prosthetic devices and minimally invasive methods for intraluminal implantation of these devices have been developed. Such prosthetic venous valve devices can be inserted intravascularly, for example from an implantation catheter. Prosthetic devices can function, for example, as a replacement venous valve, or restore native venous valve function by bringing incompetent valve leaflets into closer proximity. However, vascular devices are typically not highly responsive to conditions within the body vessel, and typically do not provide for the gradual retraction of the vessel wall over a period of hours, days or weeks.
It is desirable to find improved ways to desirably retract a body vessel wall, for example to improve the function of incompetent sphincter muscles or incompetent valves within the vessel lumen. Preferably, the implantation of a remodelable material as described herein desirably retracts a portion of the body vessel wall in a manner responsive to conditions within the body vessel while gradually narrowing a portion of the body vessel wall.